1. Field of the Invention
This invention relates to a method for acquiring azimuth information by use of GPS (Global Positioning System) satellites and to a device for acquiring azimuth information for implementing the method.
2. Description of the Prior Art
The term xe2x80x9cacquiring azimuth informationxe2x80x9d as used in this specification encompasses both the concept of xe2x80x9cazimuth determination,xe2x80x9d meaning to associate an azimuth uniquely with a specific direction, and the concept of xe2x80x9cazimuth limitation,xe2x80x9d meaning to associate a sector-shaped azimuth range defined by a start azimuth, an end azimuth and a direction of rotation with a specific direction.
Azimuth limitation will be explained first. Consider, for instance, the case of using a representation system in which angular distance (number of degrees) increases clockwise from due north defined as 0 degree. In this system, associating an azimuth of 37 degrees with the specific direction in which one sees a mountain would amount to azimuth determination. On the other hand, if one cannot obtain information of this exactness but, based on some type of information, determines the fact that the direction in question certainly falls within a sector defined by clockwise rotation between an azimuth of 35 degrees and an azimuth of 49 degrees, this would amount to azimuth limitation.
Azimuth limitation becomes a truly useful measure when it can be effected much more rapidly than azimuth determination. A system capable of either rapid azimuth limitation or precise azimuth determination, as occasion demands, has still greater utility. This is because azimuth determination can be conducted when priority is on precision and azimuth limitation be conducted when priority is on speed.
That both azimuth determination and azimuth limitation are actually necessary can be seen from the following concrete example.
Consider the case of a visually impaired person walking outdoors or of a forest ranger, surveyor or other such person who has no choice but to walk through a mountainous region in dense fog, a blizzard or other circumstances of substantially zero visibility. Any of these people would have to walk without being able to see their surroundings. Although a forest ranger or surveyor should be prepared to bivouac, either might decide to continue walking despite zero visibility if having good reason to expect a life-threatening drop in temperature after sunset or a threat to life owing to the approach of a blizzard.
Walking in zero-visibility condition (blind walking) is characterized by the following points:
First, even if a numerical azimuth value for reaching the destination can be obtained from the latitude and longitude of the current location ascertained using a mobile satellite positioning device and the known latitude and longitude of the destination, as is often possible, zero-visibility effectively deprives one of the ability to acquire general azimuth information easily by the sense of vision, so that, in the absence of some other azimuth information acquisition means, the obtained value cannot be used for effectively deciding one""s course of action. On the other hand, a compass cannot be used for determining such an important matter as the direction to walk during zero-visibility condition because, depending on the location, the direction indicated by a compass may be strongly affected by magnetic disturbance and deviate greatly from the true direction, and, moreover, is incapable of producing an output indicative of the deviation (error span). The method used by land vehicles of calculating travel direction by repositioning after a suitable amount of travel is also of no use because for this method to work the person attempting to decide the right walking direction would have to walk a distance so great as to be excessively burdensome or sometimes dangerous under condition of zero visibility. The mobile satellite positioning device, being unable to provide an azimuth, is functionally deficient as a tool for supporting a person in zero-visibility condition and incapable of vision-dependent general azimuth approximation in making appropriate walking direction decisions. A method for acquiring azimuth information that can compensate for this shortcoming is therefore necessary.
Second, even if a person should be able to decide a specific direction of travel by some method or other, the person will have difficulty maintaining the travel direction accurately in zero-visibility condition. This is because a person generally maintains a straight line of travel using a feedback loop involving fine correction of travel direction based on a direction visually perceived from a ground feature, a heavenly body or the like, but this is impossible in zero-visibility condition. Unless a person makes frequent direction checks, then, just as when walking with eyes closed, he or she will veer off the initially intended course and is liable to stray into a dangerous region such as one where avalanches are common. The required frequency of the checks is very high. A method that requires considerable work to carry out a check would therefore excessively restrict the person""s actions and be worthless from the practical viewpoint. A person walking in zero-visibility condition needs a fast method for acquiring azimuth information that can be simply implemented while continuing to walk and is suitable for frequent information acquisition.
Third, to avoid stumbling, a person who cannot rely on vision must constantly check for the presence of obstacles ahead with the hand or a stick or other extension from the hand. An azimuth determination/azimuth limitation device such as mentioned above would therefore not be very useful in a hand-carried configuration. A device to be worn on the body or clothing is therefore appropriate so as not to restrict the ability of the person walking in zero-visibility condition to grope and probe for the presence of obstacles ahead.
In view of the foregoing considerations, a device for acquiring azimuth information requires the following features for supporting blind walking. First, it must have the ability to determine azimuth with a certain degree of accuracy so as to enable a person walking in zero-visibility condition to initially decide the walking direction to the destination upon obtaining the latitude and longitude of the current location and the destination. Second, to enable a person walking in zero-visibility condition to frequently check whether or not his or her direction of travel deviates from the intended direction, it must be capable of rapid and simple measurement and, further include an azimuth limitation function capable of indicating degree of error. Third, since a person walking in zero-visibility condition strongly needs free use of the hands for discerning obstacles ahead and avoiding falls, it is preferably structured to be worn directly on the body or clothing.
An object of the present invention is therefore to provide a method and device for acquiring azimuth information in zero-visibility condition.
Another object of the present invention is to provide a device for acquiring azimuth information that can be readily worn on the body or clothing.
For achieving these objects, this invention provides a method for acquiring azimuth information comprising:
a step of disposing a pair of planar antennas each having a hemispherical antenna pattern for GPS satellite signals back-to-back, parallel to each other and vertical, whereby each planar antenna forms a sky coverage area of antenna sensitivity that is a sky quarter-sphere in a direction the antenna faces;
a step of causing a pair of GPS receivers, one connected to each antenna, to scan signals transmitted by GPS satellites in the sky hemisphere;
a step of causing the GPS receivers to output respective channel statuses indicating reception of the signal transmitted by each GPS satellite in the sky hemisphere;
a step of causing at least one GPS receiver to output satellite azimuth for each GPS satellite in the sky hemisphere;
a step of discriminating the sky coverage area in which each GPS satellite that transmitted the signal is present, based on a comparison of the channel statuses in the GPS receivers;
a step of arranging results of the discriminating step in a ring-like sequence of a specific rotational direction, utilizing the satellite azimuths as indices; and
a step of limiting a measurement direction to be ascertained as a value in an azimuth range defined by a start azimuth, an end azimuth and an orientation of rotation based on information contained in the ring-like sequence of discrimination results obtained in the arranging step.
In the method just mentioned above, the planar antennas may be planar patch antennas.
In the foregoing method, when a signal of a certain GPS satellite is synchronized with by a corresponding pseudo random noise code in a channel of one GPS receiver and the same signal is not synchronized with by a corresponding pseudo random noise code in a channel of the other GPS receiver, discrimination that the certain GPS satellite is present in the antenna sky coverage area formed by the antenna 40 connected to the one GPS receiver is conducted.
In the foregoing method, when the ring-like sequence of discrimination results consists of one finite sequence which consists of one or more continuous terms indicating presence in the coverage area of one planar antenna, no or one finite sequence which consists of one or more continuous terms indicating presence in the coverage area of the other planar antenna, and no finite sequence which consists of one or more continuous terms indicating presence at a boundary between the antenna coverage areas, the azimuth of the measurement direction to be ascertained is limited in the azimuth range, based on satellite azimuths associated with a first term and a last term in the one or two finite sequences and an initial assumption on geometry among the antennas and the measurement direction.
In the foregoing method, the antennas can be disposed, one on either side of a user""s head or body.
The present invention further provides a method for acquiring azimuth information, comprising:
a step of disposing a pair of planar antenna each having a hemispherical antenna pattern for GPS satellite signals back-to-back, parallel to each other and vertical, whereby each planar antenna forms a sky coverage area of antenna sensitivity that is a sky quarter-sphere in a direction the antenna faces;
a step of horizontally rotating the antennas;
a step of causing a pair of GPS receivers, one connected to each antenna, to scan signals transmitted by GPS satellites in the sky hemisphere;
a step of causing the GPS receivers to output respective channel statuses indicating reception of the signal transmitted by each GPS satellite in the sky hemisphere;
a step of causing at least one GPS receiver to output satellite azimuth for each GPS satellite in the sky hemisphere;
a step of stopping the horizontal rotation of each antenna when the antenna reaches an orientation whereat discrimination is conducted that at least one GPS satellite is present at a boundary between the sky coverage areas of the antennas;
a step of discriminating, with regard to remaining GPS satellites, the sky coverage area in which a GPS satellite that transmitted the signal is present, based on a comparison of the channel statuses;
a step of arranging results of the discriminating step in a ring-like sequence of a specific rotational direction, utilizing the satellite azimuths as indices; and
a step of determining an azimuth of a measurement direction to be ascertained based on information contained in the ring-like sequence of discrimination results obtained in the arranging step.
In the method just mentioned above, the planar antennas may be planar patch antennas.
In the foregoing method, when a signal of a certain GPS satellite is synchronized with by a corresponding pseudo random noise code in channels of the GPS receivers, discrimination that the certain GPS satellite is present at a boundary between the sky coverage areas of the antennas is conducted.
In the foregoing method, when the ring-like sequence of discrimination results consists of one first-finite sequence which consists of one or more continuous terms indicating presence in the coverage area of one planar antenna, no or one second-finite sequence which consists of one or more continuous terms indicating presence in the coverage area of the other planar antenna, one third-finite sequence which consists of one or more continuous terms indicating presence at one direction on a boundary between the antenna coverage areas, and no or one fourth-finite sequence which consists of one or more continuous terms indicating presence at the other direction on the boundary between the antenna coverage areas, the azimuth of the measurement direction to be ascertained is determined based on satellite azimuths associated with terms in the one first-finite sequence and the one third-finite sequence, and an initial assumption on geometry among the two antennas and the measurement direction.
In the foregoing method, the antennas can be disposed, one on either side of a user""s head or body.
The present invention also provides a device for acquiring azimuth information comprising:
a pair of planar antennas each having a hemispherical antenna pattern for receiving signals transmitted by GPS satellites, disposed back-to-back, parallel to each other and vertical, whereby each planar antenna forms a sky coverage area of antenna sensitivity that is a sky quarter-sphere in a direction the antenna faces;
a pair of receivers, one connected to each antenna, for receiving signals transmitted by GPS satellites present in the sky coverage areas, conducting positioning concomitantly with calculating azimuths of all satellites, and outputting channel statuses;
means for discriminating which sky coverage area in which each GPS satellite transmitting a signal is present, based on a comparison of the channel statuses in the receivers;
means for arranging results output by the discriminating means in a ring-like sequence of a specific rotational direction based on satellite azimuth information acquired from at least one of the receivers; and
means for limiting an azimuth of a measurement direction to be ascertained in an azimuth range which is defined by a start azimuth, an end azimuth and an orientation of rotation and determining the azimuth of the measurement direction to be ascertained as a value, both based on information derived from the thus obtained ring-like sequence of discrimination results.
In the device, the arranging means may be means including as indices satellite azimuths calculated concomitantly with positioning.
In the device, the antennas can be disposed, one on either side of a user""s head or body.
The device can further comprise means for horizontally rotating the antennas at a constant speed within the azimuth range.
Being constituted in the foregoing manner, the present invention can provide support for the everyday outdoor activities or outdoor work activities of a visually impaired person and can also offer various kinds of help to normal, unimpaired persons working outdoors under poor visibility conditions. Some of the benefits provided by the invention include:
(1) Azimuth limitation and azimuth determination helpful for carrying out everyday activities can be provided by one and the same device. The first of these functions, azimuth limitation, can be executed straightaway with substantially zero wait time. (This is particularly useful for a visually impaired person during walking because such a person needs to confirm the direction of advance with high frequency to stay on a straight course.) The second function, azimuth determination, enables the user to acquire exact azimuth information simply by turning the antennas within a limited degree of rotation. (This function provides the precise directional information that a visually impaired person needs for deciding what action to take.)
(2) The device can be implemented in a compact, lightweight configuration that can be worn on the head or clothing during use.
(3) The device can be fabricated at relatively low cost using inexpensive components commercially available for fabricating portable satellite positioning equipment.
(4) The device can be given an appearance readily acceptable by visually impaired persons for use (wearing) in public places.
(5) When the patch antennas are fitted on the user""s head or body, the user can easily select the direction whose azimuth is to be measured because the measured direction coincides with the direction in which the user""s face or body is directed. Operation is therefore direct and intuitive and there is no need to convert the acquired azimuth information to that for the direction of interest.
(6) The device eliminates the need to carry a satellite positioning device and a device for acquiring azimuth information as separate units, thus reducing the number and bulk of the articles that need be carried. This is particularly advantageous for outdoor activities that limit the amount of gear that can be taken along.